A report by three top climate think-tanks says efforts planned by New Zealand to cut greenhouse gases stack up better than the European Union's - the region normally thought of as a climate leader.
But an analysis by Sustainability Council director Simon Terry found the New Zealand ranking was "wildly inaccurate" because it assumed countries would make real cuts to their emissions and not mop them up with forest sinks.
The study tracks the progress of climate talks by measuring targets announced by countries against a goal of keeping warming to less than 2C.
Ecofys, Climate Analytics and the European Climate Foundation recently added up the major pledges for greenhouse gas cuts and found the world was headed for more than 3C warming by 2100 and had at least a one in four chance of warming more than 4C.
Scientists and analysts for the Climate Action Tracker then ranked the countries according to how their targets measured up against a "fair" share.
Countries were ranked from "role model", through "sufficient" to "medium" and finally "inadequate".
After taking into account how hard it would be to meet its target, New Zealand's pledge of 10-20 per cent below 1990 levels by 2020 was ranked medium - better than most countries including the EU nations, whose promise to cut emissions by 20-30 per cent was ranked "inadequate".
The study found that of the developed countries only Japan and Norway's efforts were "sufficient".
Of all countries only two - Costa Rica and the Maldives - were rated as role models.
International Climate Change Negotiations Minister Tim Groser said in a speech last week that the rankings showed New Zealand was in "respectable territory" although it was not "top of the class". He has said New Zealand could not expect to come out top because of its unique challenges, with agriculture and already-high rates of renewable energy.
A glossary to the report explains New Zealand's medium rating means its target was in the weakest third of the range of targets that could be considered fair based on international studies.
If all countries were in the medium category the world would not be able to limit greenhouse gases enough to keep warming within 2C, said the authors.
The authors noted their assessment of New Zealand was "clouded" because its targets were conditional on changes to forestry rules and having access to international carbon markets.
Forest credits are important to New Zealand and the rules on them could make the difference between committing to a 10-20 per cent emissions cut or not.
Mr Terry, who is in Copenhagen for the climate talks, said the report assumed countries would make real emissions cuts to meet their targets but New Zealand was counting heavily on offsetting its emissions using carbon sinks from swathes of crop forests. Many of those forests would be harvested in the 2020s, leaving the planet no better off, he said.
When that was taken into account New Zealand's level of effort slipped to "inadequate", he said.
Catherine Beard, executive director of industry lobby group the Greenhouse Policy Coalition, said it did not matter how New Zealand met its targets as long as they were met. If forests were chopped and not replanted it could buy carbon credits abroad.
A background report to the climate action tracker said it had assumed forestry and land use rules would stay the same. But New Zealand negotiators have reserved the right not to cut emissions unless there are rule changes.
Meanwhile, ministers including Mr Groser met on Sunday with Danish delegates to try to make progress on a draft climate pact in the hope of reaching a broad-brush agreement by Friday.